Stabilizers for the stabilization of unsaturated hydrocarbon-based precursor

ABSTRACT

A stabilized composition consists essentially of unsaturated hydrocarbon-based materials, and a stabilizer selected from the group consisting of a hydroxybenzophenone and a nitroxyl radical based stabilizer. A method for stabilizing unsaturated hydrocarbon-based precursor material against the polymerization comprises providing a stabilizer selected from the group consisting of a hydroxybenzophenone and a nitroxyl radical based stabilizer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/038,409, filed Feb. 27, 2008 now U.S. Pat. No. 7,968,001;which claims benefit of U.S. Provisional Application No. 61/015,028,filed Dec. 19, 2007. The disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

Future generations of dielectric films utilize porogens in combinationwith organosilicates precursors to produce porous low k films. For thispurpose saturated or unsaturated hydrocarbon-based porogens areco-deposited with the organosilicate to produce the initial compositefilm, comprising a mixture of organosilicate precursor and organicporogen. This film is subsequently subjected to various treatmentmethods to decompose the porogen. During this curing process the porogenbyproducts are liberated as gaseous species leaving behind anorganosilicate matrix containing voids in the spaces vacated by theporogen. The resulting voids or air pockets have an intrinsic dielectricconstant of unity which has the effect of decreasing the overalldielectric constant of the porous solid below that of the dense matrixmaterial.

Other areas in which organic precursors are being used in themicroelectronics industry are the deposition of carbon hardmasks and thedeposition of anti-reflective coatings. These films are deposited byplasma enhanced chemical vapor deposition (PECVD) using hydrocarbonprecursors, especially unsaturated organic hydrocarbons.

Unsaturated hydrocarbon-based materials have been evaluated for use as aporogen precursor to be used along with an appropriate organosilicateprecursor for the deposition of porous low k films.

However, many unsaturated hydrocarbons that are prone to polymerizationwill gradually degrade or polymerize at ambient temperature or atmoderate temperatures that are often encountered during normalprocessing, purification or application of the particular chemical. Theprior art discloses a variety of chemicals used to stabilizehydrocarbon-based porogens against the polymerization of olefinichydrocarbons, including several broad classes of organic compounds suchas phenols, amines, hydroxylamines, nitro compounds, quinine compoundsand certain inorganic salts. An example of this would be monomers suchas butadiene and isoprene which are well known to undergo gradualpolymerization in storage tanks or during transportation at ambienttemperatures.

Some of unsaturated hydrocarbon-based precursor materials are describedin U.S. Pat. No. 6,846,515, commonly assigned to the assignee of thepresent invention, which is incorporated by reference herein in itsentirety.

2,5-Norbornadiene (NBDE) is one of the leading materials being evaluatedas a precursor for porogen, carbon hardmask and antireflective coating,for the production of low dielectric constant films using chemical vapordeposition (CVD) methods. Isoprene is a promising precursor for thedeposition of carbon hardmasks and antireflective coatings. However,NBDE and isoprene are thermally unstable with respect tooligomerization/polymerization.

NBDE and isoprene degrade at a substantial rate at ambient temperatureto form soluble NBDE and isoprene oligomeric degradation products.Isoprene is also known to undergo a relatively rapid dimerizationreaction. Hence, the concentration of dissolved oligomers in NBDE andisoprene are expected to gradually increase over time during theirtransport and storage prior to their utilization as a precursor fordielectric materials. Furthermore, the soluble oligomers willimmediately precipitate upon contact with a more polar liquid such asdiethoxymethylsilane (DEMS). This instability is expected to causeprecursor delivery problems and film quality issues.

Chemical vendors commonly supply NBDE with 100-1000 parts per million(ppm) of 2,6-di-tert-butyl-4-methylphenol, also known as butylatedhydroxytoluene or by the acronym BHT. BHT is currently used as theindustry standard to slow the rate of NBDE degradation for transport andstorage purposes. However, BHT has limited efficacy to suppress NBDEdegradation.

A recently published US Patent Application 20070057235 by Teff et al.taught the use of phenolic antioxidants for the stabilization of NBDE.

In order for NBDE or isoprene to be viable in a manufacturingenvironment it is critical that the oligomer (i.e., non-volatileresidue) content is minimized to avoid processing issues and to allowmanufacturers to meet the demanding film quality specifications as setby the semi-conductor industry.

This invention discloses effective stabilizers which can be used to slowdown the rate of degradation for the unsaturated hydrocarbonsprecursors, thereby mitigating the potential process and film qualityissues which can result from precursor instability, thus, increasing theviability of such materials for application as precursors for porogens,carbon hardmask materials and antireflective coatings for the productionof high quality low dielectric constant films.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the present invention is a stabilized compositionconsisting essentially of an unsaturated hydrocarbon-based precursormaterial, and a stabilizer selected from the group consisting of ahydroxybenzophenone based stabilizer and a nitroxyl radical basedstabilizer.

Another embodiment of the present invention is a stabilized composition,consisting essentially of an unsaturated hydrocarbon-based material, atleast one polar liquid and a stabilizer selected from the groupconsisting of a hydroxybenzophenone based stabilizer, a nitroxyl radicalbased stabilizer and a hydroquinone based stabilizer.

Another embodiment of the present invention is a stabilized composition,consisting essentially of 2,5-Norbornadiene (NBDE), and a stabilizerselected from the group consisting of a hydroxybenzophenone basedstabilizer and a nitroxyl radical based stabilizer.

Yet, another embodiment of the present invention is a method forstabilizing an unsaturated hydrocarbon-based precursor material againstpolymerization. The method comprises providing a stabilizer selectedfrom the group consisting of a hydroxybenzophenone based stabilizer anda nitroxyl radical based stabilizer.

Yet, another embodiment of the present invention is a method forstabilizing 2,5-Norbornadiene (NBDE) against its polymerizationcomprising providing a stabilizer selected from the group consisting ofa hydroxybenzophenone based stabilizer and a nitroxyl radical basedstabilizer.

Yet, another embodiment of the present invention is a method forstabilizing an unsaturated hydrocarbon-based precursor againstprecipitation of solids upon contact of the unsaturated hydrocarbon withat least one polar liquid, comprising

(a) adding to the unsaturated hydrocarbon-based precursor a stabilizerselected from the group consisting of a hydroxybenzophenone basedstabilizer, a nitroxyl radical based stabilizer and a hydroquinone basedstabilizer; and

(b) contacting mixture in (a) with the at least one polar liquid.

For the embodiments above,

the unsaturated hydrocarbon-based precursor material can have bothcyclic or non-cyclic structure, wherein the cyclic structure is selectedfrom the group consisting of (a) at least one singly or multiplyunsaturated cyclic hydrocarbon having a formula C_(n)H_(2n−2x), whereinx is a number of unsaturated sites, n is from 4 to 14, the number ofcarbons in the cyclic structure is between 4 and 10; and (b) at leastone multiply unsaturated bicyclic hydrocarbon having a formulaC_(n)H_(2n−(2+2x)), wherein x is a number of unsaturated sites, n isfrom 4 to 14, the number of carbons in the bicyclic structure is from 4to 12;

the hydroxybenzophenone based stabilizer is represented by a structureof:

wherein at least one member of the group R¹ through R¹⁰ is hydroxyl, theremaining R¹ through R¹⁰ is independently selected from the groupconsisting of hydrogen, hydroxyl, C₁-C₁₈ linear, branched or cyclicalkyl, C₁-C₁₈ linear, branched or cyclic alkenyl, C₁-C₁₈ linear,branched or cyclic alkoxy, substituted or unsubstituted C₄-C₈ aryl andcombinations thereof;

the nitroxyl radical based stabilizer is represented by a structurehaving at least one NO group:

wherein:raised period “•” denotes one unpaired electron;R¹ through R⁴ are independently selected from a straight chained orbranched, substituted or unsubstituted, alkyl or alkenyl group having achain length sufficient to provide steric hinderance for the NO group;wherein the substituted group comprises oxygen-containing groupsselected from the group consisting of hydroxyl, carbonyl, alkoxide, andcarboxylic group; andR⁵ and R⁶ are independently selected from a straight chained orbranched, a substituted or unsubstituted, alkyl group or alkenyl group.

Further for some of the embodiments above, the unsaturatedhydrocarbon-based precursor material is selected from the groupconsisting of 2,5-Norbornadiene (NBDE) and isoprene; the nitroxylradical based stabilizer is selected from the group consisting of2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO),4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (4H-TEMPO) andcombinations thereof; the hydroxybenzophenone based stabilizer isselected from the group consisting of 2-hydroxy-4-methoxy-benzophenone(2H4MB), 2,4-dihydroxybenzophenone (24DHB),2,2′-dihyroxy-4-methoxybenzophenone (22DH4MB) and combinations thereof;the hydroquinone based stabilizer is selected from the group consistingof methyl hydroquinone (MHQ), hydroquinone monomethyl ether (HQMME) andcombinations thereof; and the at least one polar liquid is selected fromthe group consisting of diethoxymethylsilane (DEMS), isopropanol (IPA)and the mixture thereof.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1. Solids-probe mass spectrum of non-volatile residue collectedfrom evaporation of an aged sample of NBDE.

FIG. 2. The effect of different stabilizers from the present inventionon the degradation rate of NBDE at 80° C.

FIG. 3. The effect of different stabilizers on the degradation rate ofNBDE at 80° C.; the stabilizers from the present invention were shown onthe right and the stabilizers used in prior art were shown on the left.

DETAILED DESCRIPTION OF THE INVENTION

The unsaturated hydrocarbon-based precursor material can be cyclicunsaturated hydrocarbon-based.

The cyclic unsaturated hydrocarbon-based precursor material can besingly or multiply unsaturated cyclic hydrocarbon having a cyclicstructure and the formula C_(n)H_(2n−2x), where x is the number ofunsaturated sites, n is 4 to 14, the number of carbons in the cyclicstructure is between 4 and 10, and at least one singly or multiplyunsaturated cyclic hydrocarbon optionally contains a plurality of simpleor branched hydrocarbons substituents substituted onto the cyclicstructure, and contains unsaturation inside endocyclic or on one of thehydrocarbon substituents. Examples include cyclohexene,vinylcyclohexane, dimethylcyclohexene, t-butylcyclohexene,alpha-terpinene, pinene, 1,5-dimethyl-1,5-cyclooctadiene, andvinyl-cyclohexene.

The cyclic unsaturated hydrocarbon-based precursor material can also bemultiply unsaturated bicyclic hydrocarbons of the general formulaC_(n)H_(2n−(2+2x)) where x is the number of unsaturated sites in themolecule, n=4-14, where the number of carbons in the bicyclic structureis between 4 and 12, and where there can be a plurality of simple orbranched hydrocarbons substituted onto the cyclic structure. Theunsaturation can be located inside endocyclic or on one of thehydrocarbon substituents to the cyclic structure. Examples includecamphene, norbornene, norbornadiene, etc.

The unsaturated hydrocarbon-based precursor material can also benon-cyclic, such as linear hydrocarbon-based. An example of non-cyclicunsaturated hydrocarbon-based precursor material is isoprene.

Preferably, NBDE and isoprene are selected as the precursors for theproduction of low k dielectric materials.

NBDE (2,5-Norbornadiene) is a particularly attractive precursorcandidate because of its high degree of chemical unsaturation which isbelieved to give rise to favorable deposition properties such as highdeposition rates and high utilization efficiencies. The utilizationefficiency pertains to the amount of hydrocarbon porogen precursorrequired relative to the organosilicate precursor in order to deposit aporous low k film of a given dielectric constant. Unfortunately, thehigh degree of unsaturation of NBDE may also be responsible for itsintrinsic thermal instability with respect to oligomerization.

Laboratory evaluation has shown that NBDE degrades at ambienttemperature to form soluble oligomeric species. The degradation productshave been identified by solids-probe mass spectrometry to be a mixtureof NBDE oligomers, including various dimers, trimers, tetramers,pentamers, hexamers, etc. shown in FIG. 1.

The degradation of NBDE raises a number of issues for its application asa precursor for making low k films. The high rate of degradationsuggests that the chemical composition and physical properties of theprecursor will change over time. Such changes are likely to have asignificant impact on the properties of the resulting film, making itdifficult for end users to produce a consistent quality film thatconforms to the rigorous production specifications of thin filmmanufacturers.

A second problem posed by the NBDE and isoprene degradation is relatedthe chemical delivery method commonly used for such liquid precursors.Volatile liquids such as NBDE and isoprene are often delivered by atechnique referred to in the industry as DLI, or direct liquidinjection. For DLI systems the precursor is delivered to the tool at aprecisely metered rate as a liquid through an injector port into theheated injection manifold. The manifold is operated at elevatedtemperature and reduced pressure to cause the precursor to rapidlyvaporize. Once vaporized, the gaseous precursor is delivered to thedeposition chamber. The DLI delivery method will indiscriminatelytransfer the NBDE or isoprene liquid along with any dissolved oligomericdegradation products to the tool. The oligomers are expected to beeither less volatile or non-volatile under the temperature and pressureconditions of the heated injection manifold. The delivery of lowvolatility oligomeric components would result in the gradualaccumulation of said species in the tool plumbing which is expected tohave a detrimental impact on tool operation and/or film quality.

A third possible negative consequence of using degraded NBDE is relatedto possible on-tool precipitation issues that may result from contact ofpartially degraded NBDE with a more polar chemical, such as DEMS(diethoxymethylsilane). Instantaneous precipitation of the oligomers isexpected to occur if NBDE containing an appreciable concentration ofdissolved oligomeric degradation products comes into contact with asubstantial amount of a more polar liquid, such as an alcohol or analkoxysilane such as DEMS. This effect is demonstrated in Examples 24,25 and 30. The precipitation is believed to be caused by an increase inthe overall polarity of the liquid blend that occurs when a substantialquantity of DEMS is added to NBDE. On-tool precipitation is expected tooccur in the event that NBDE, containing oligomeric degradationproducts, comes into contact with a more polar component, such as DEMS,during the co-deposition of porogen and silica source materials. Suchon-tool precipitation would cause increased tool down-time and/ornecessitate more frequent tool preventative maintenance in order toavoid precursor plugging or flow problems. Oligomer precipitation mayalso cause indirect problems by adversely impacting film quality, and/orincreasing on-wafer particle count, etc.

In order for precursor materials to be viable in a manufacturingenvironment they need to satisfy practical requirements with respect toproduct shelf-life. The product shelf life provides the end user ormanufacturer assurance that the subject chemical will meet certainminimal standards of performance if used within the time allotted by theshelf-life specification. In practice the product shelf life is oftendefined by the length of time a chemical will meet pre-determined purityrequirements with respect to key chemical components. The rate of NBDEand isoprene degradation must be reduced to an acceptable level toensure that they conform to minimal shelf-life criteria, and as such,will be viable in a manufacturing environment as precursors for theproduction of low k films.

Our laboratory tests have shown that NBDE degrades in the mannerpreviously described at a rate of ˜1.4 wt. % per year at ambienttemperature, which corresponds to 1.6 ppm per hour. At 80° C. the rateof degradation increases 160-fold to 258 ppm/hr. Spiking NBDE with 200ppm of BHT (usually provided by the chemical vendors) will reduce itsrate of degradation by only 31%, such that it degrades at 179 ppm/hr at80° C. Therefore, although BHT does slow down the degradation rate ofNBDE, it does not slow it down enough to make it practical for use inthe current application. These experiments are described in Examples 2-4and summarized in Table 1 and FIGS. 2 and 3.

Our laboratory testing of the stabilizers MHQ and HQMME specified in USPatent Application 20070057235 by Teff et al. showed that they wereindeed more effective than BHT for inhibiting polymerization of NBDE.For example, 200 ppm of MHQ decreased the degradation rate NBDE to 53ppm per hour at 80° C.; 200 ppm of HQMME was slightly more effectivedropping the degradation rate to 47 ppm per hour at 80° C. Theserepresent 79% and 82% reduction, respectively, in the rate ofdegradation relative to the unstabilized NBDE. MHQ and HQMME were thusconfirmed to be more effective than BHT for stabilizing NBDE, the samelevel of the latter inhibitor only decreased the NBDE degradation rateby 31% under comparable test conditions. Therefore, although MHQ andHQMME were more effective than BHT, they also have limited ability tosuppress the oligomerization of NBDE, and as such, have limited utilityfor the stabilization of NBDE for the current application. Theseexperiments are described in Examples 4, 7 and 9 and summarized in Table1 and FIG. 3.

In the present invention two classes of materials are disclosed whichare very effective for stabilizing NBDE. These two classes of materialsare: hydroxybenzophenones and nitroxyl radicals. These two classes ofinhibitors, unlike the quinones or phenolic antioxidants, do not requirethe presence of oxygen in order to be optimally effective.

The first class of stabilizers is known as hydroxybenzophenones. Thehydroxybenzophenones are known to be light stabilizers which are activeUV absorbers. They are not known for their ability to suppress theoligomerization reaction of thermally unstable unsaturated hydrocarbons.This class of stabilizers is represented by the following structure:

where at least one member of the group R¹ through R¹⁰ is OH, theremaining R¹ through R¹⁰ can each be hydrogen, hydroxyl, C₁-C₁₈ linear,branched, or cyclic alkyl, C₁-C₁₈ linear, branched, or cyclic alkenyl,C₁-C₁₈ linear, branched, or cyclic alkoxy, or substituted orunsubstituted C₄-C₈aryl. Suitable examples of R¹ through R¹⁰ may includebut are not limited to hydrogen, hydroxyl, methyl, ethyl, n-propyl,n-butyl, iso-propyl, iso-butyl, tert-butyl, methoxy, ethoxy, propoxy,iso-propoxy, butoxy, iso-butoxy or tert-butoxy.

Suitable examples of the hydroxybenzophenone based stabilizers mayinclude but are not limited to 2-hydroxy-4-(n-octyloxy)benzophenone,2-hydroxy-4-methoxybenzophenone (2H4MB), 2,4-dihydroxybenzophenone(24DHB), 2-hydroxy-4-(n-dodecyloxy)benzophenone,2,2′-dihyroxy-4-methoxybenzophenone (22DH4MB),2,2′-dihydroxy-4,4′-dimethoxybenzophenone,2,2′,4,4′-tetrahydroxybenzophenone, 4-hydroxybenzophenone and anycombination thereof.

Examples of preferred hydroxybenzophenones are2-hydroxy-4-methoxy-benzophenone (2H4MB), 2,4-dihydroxybenzophenone(24DHB), and 2,2′-dihyroxy-4-methoxybenzophenone (22DH4MB).

The amount of the stabilizer is preferably from 1 to 5000 parts permillion (ppm), more preferably 5 to 1000 ppm, and most preferable 20 to200 ppm.

In preferred embodiments, NBDE or isoprene is selected as theunsaturated hydrocarbon-based precursor for the production of low kdielectric materials; 2-hydroxy-4-methoxy-benzophenone,2,4-dihydroxybenzophenone, or 2,2′-dihyroxy-4-methoxybenzophenone isselected as the hydroxybenzophenone based stabilizer. The amount of thestabilizer is from 20 to 200 ppm. The stabilizers in the preferredembodiments described herein, are shown to be considerably moreeffective at suppressing the rate of degradation than those disclosed inthe prior art, and as such, increase the likelihood of the successfulcommercial implementation of the precursors for the production of low kdielectric materials.

The second class of stabilizers known as nitroxyl radicals isrepresented by the following structure:

Such nitroxyl radical compounds have at least one NO,wherein

the raised period “•” denotes one unpaired electron,

the nitrogen atom is further bound to two carbon atoms,

R¹ through R⁴ are the same or different, straight chained or branched,substituted or unsubstituted, alkyl or alkenyl groups of a chain lengthsufficient to provide steric hinderance for the NO group, in which thesubstituted constituents may comprise oxygen-containing groups such ashydroxyls, carbonyls, alkoxides, carboxylic groups, includingsubstituted groups, thereof;

R⁵ and R⁶ are the same or different, straight chained or branched,substituted or unsubstituted, alkyl or alkenyl groups, which may befurther connected by various bridging groups to form cyclic structures,such as, which may have fused to it another saturated, partiallyunsaturated or aromatic ring, in which any of the aforementioned cyclicor ring structures may possess ring substituents such as straight chainor branched alkyl groups or oxygen-containing groups such as hydroxyls,carbonyls, alkoxides, carboxylic groups, including substituted groups,thereof.

Suitable examples of R¹ through R⁴ include but are not limited tomethyl, ethyl, n-propyl, n-butyl, n-pentyl, iso-propyl, iso-butyl,iso-pentyl, tert-butyl, neo-pentyl, octadecyl, propenyl, butenyl,pentenyl, and the like.

Suitable examples of R⁵ and R⁶ include but are not limited to methyl,ethyl, n-propyl, n-butyl, n-pentyl, iso-propyl, iso-butyl, iso-pentyl,tert-butyl, neo-pentyl, octadecyl, ethenyl, propenyl, butenyl, pentenyl,or R⁵ and R⁶ may constitute part of a cyclic structure, such as the6-membered piperidines, 5-membered pyrrolidones and the like, examplesof which are provided below. These ring structures may be substituted.

Suitable examples of the nitroxyl radical based stabilizers include butare not limited to 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (4H-TEMPO), di-tert-butylnitroxyl, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-one,1-oxyl-2,2,6,6-tetramethylpiperidin-4-ylacetate,1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 2-ethylhexanoate,1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl stearate,1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl benzoate,1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 4-tert-butylbenzoate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)succinate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)sebacate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)n-butylmalonate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)phthalate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)isophthalate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)terephthalate,bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)hexahydroterephthalate,N,N′-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipamide,N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-caprolactam,N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-dodecylsuccinimide,2,4,6-tris(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl isocyanurate,2,4,6-tris-[N-butyl-N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl]-s-triazine,and 4,4′-ethylenebis(1-oxyl-2,2,6,6-tetramethylpiperazin-3-one).

Examples of preferred nitroxyl radicals are TEMPO and 4H-TEMPO. Thestructures of these two compounds are shown below.

The amount of the stabilizer is preferably from 1 to 5000 parts permillion (ppm), more preferably 5 to 1000 ppm, and most preferable 20 to200 ppm.

In preferred embodiments, NBDE or isoprene is selected as theunsaturated hydrocarbon-based precursor for the production of low kdielectric materials and TEMPO or 4H-TEMPO is selected as the nitroxylradical based stabilizer. The amount of the stabilizer is from 20 to 200ppm. The stabilizers in the preferred embodiments described herein, areshown to be considerably more effective at suppressing the rate ofdegradation of NBDE than those disclosed in the prior art, and as such,increase the likelihood of its commercial implementation for theproduction of porous low k dielectric materials.

WORKING EXAMPLES

In order to more fully describe the present invention, the followingexamples are presented which are intended to be merely illustrative andnot in any sense limitative of the invention.

NBDE degrades at a substantial rate at ambient temperature formingsoluble oligomeric byproducts. The degradation may or may not result inthe discoloration of the NBDE liquid. The extent of degradation isassessed by determining the concentration of oligomers in the NBDEliquid. However, gas chromatography, the most common chemical analysismethod used for organic liquids, is not an effective method forquantifying the amount of oligomers in NBDE solution. The oligomerscannot be accurately quantified by GC because they are reactive and, assuch, they are prone to further oligomerization. They are also generallynon-volatile because of their high molecular weight causing them toelute from the GC column only after very long retention times or perhapsnot at all.

A non-volatile residue test has been developed to reliably measure theamount of oligomers in NBDE solution. To perform this evaluation NBDE isevaporated by purging the NBDE container with a high purity inert gas,such as helium, leaving behind the non-volatile residue components. Thecontainer may be heated slightly during the evaporation step in order toobtain a stable final weight. The weight of the non-volatile residue,thus determined, is used as a measure of the amount of oligomers insolution, and hence, an indication of the extent of degradation of NBDE.This general method is described in further detail in Example 1.

Unstabilized NBDE degrades at a rate of approximately 1.4% per year atambient temperature. This corresponds to about 270 ppm per week or about1.6 ppm per hour. In order to assess the relative degradation within apractical period of time, various samples of unstabilized and stabilizedNBDE were subjected to standardized accelerated aging test conditions.This test consisted of distilling the NBDE to remove any non-volatiledegradation products. Within 24 hours the distilled NBDE was placed intoquartz containers as described below, and heated to 60-80° C. for 6-7days. After this time the containers were cooled to room temperature andthe amount of degradation was determined. In this manner variousstabilizers were assessed according to their relative ability tosuppress the degradation of NBDE. Examples 2-23, illustrate themeasurement of non-volatile residue (i.e., the extent of degradation)for various samples of neat and stabilized NBDE. The NBDE used inExample 2 was aged at room temperature. The NBDE evaluated in Examples3-23 was subjected to accelerated aging conditions as described herein.

Example 1 Residue Evaluation of Recently Distilled NBDE

A sample of NBDE was flash distilled to remove non-volatile impuritiesusing a rotary-evaporator. The distilled material was analyzed by GC tohave a nominal purity of 99.4%. The tare weight of an empty, clean 1.2liter quartz bubbler was recorded after evacuation. The bubbler waspreviously equipped with gas inlet and outlet ports, each fitted with aTeflon valve. The bubbler inlet port had a dip-tube that extends towithin ⅛″ of the base of the container. About 600 g of NBDE was added tothe quartz bubbler within a nitrogen-containing dry box. The bubbler wasre-weighed to determine the weight of the NBDE. A cylinder of researchgrade He was connected to the bubbler inlet line. The bubblertemperature was increased to 35° C. to increase the vapor pressure ofthe NBDE. He was purged through the bubbler at a flow rate of 3.0 SLPM(standard liters per minute) for 4 hours to evaporate the NBDE. At thistime the bubbler temperature was raised to 80° C. and the bubbler wasevacuated for 2.0 hours to achieve a stable weight. This experiment wasdone in duplicate. The weights of the non-volatile residue for the tworuns were 0.59 g and <0.01 g, corresponding to an average residue of0.05 wt. %. The experimental results are summarized in Table 1.

Example 2 Evaluation of the Degradation Rate of NBDE Stored at AmbientTemperature

A 13.0 liter sample of NBDE was purified by atmospheric distillation.The distilled sample was analyzed by GC to have a nominal purity of99.4%. The sample was stored in a chemical cabinet indoors for a totalof 287 days. At this time approximately 200 g of NBDE was loaded into apre-cleaned, pre-tared bubbler as described in Example 1. The bubblerwas subjected to 3.0 SLPM at 35° C. for 4.0 hours to evaporate the NBDE.The bubbler temperature was raised to 80° C. and the bubbler wasevacuated for 2.0 hours to achieve a stable weight. The final weight ofthe bubbler was recorded after the evacuation step to determine theweight of the non-volatile residue. This experiment was done induplicate. The weights of the non-volatile residue for the two runs were2.29 g and 2.24 g, corresponding to an average residue of 1.12 wt. %.This is equivalent to a degradation rate of 1.63 ppm per hour based onthe weight of the residue and the 287 days of aging. The experimentalresults are summarized in Table 1.

Example 3 Evaluation of the Degradation Rate of Unstabilized NBDE UsingAccelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. Approximately 150-200 g of the distilled NBDEwas loaded into a cleaned, pre-tared bubbler as described in Example 1.The bubbler was placed into an oven and held at 80° C. for 7 days. Thetemperature of 80° C. was chosen for this study for two reasons: (1) 7days at 80° C. is intended to simulate the amount of degradation thatwould occur if the sample were allowed to age at ambient temperature for1 year, assuming that the degradation rate follows a simple Arrheniustype behavior of doubling for every temperature increase of 10° C.; and(2) 80° C. is a common temperature for the heated manifold used tovaporize precursors prior to the mixing bowl and/or deposition chamberin chemical vapor deposition hardware. The quartz bubbler was removedfrom the 80° C. oven after 7 days. The bubbler was held at 35° C. whilepurging with 3 SLPM of He for 6 hours. At this time the bubblertemperature was raised to 80° C. and the bubbler was evacuated for 2.0hours to achieve a stable weight. The final weight of the bubbler wasrecorded after the evacuation step to determine the weight of thenon-volatile residue. This experiment was run a total of 6 times, sinceit was used as the “control” for the evaluation of various stabilizers.The average non-volatile residue for these runs was 4.33 wt. %,corresponding to a degradation rate of 258 ppm per hour at 80° C. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 4 Evaluation of the Degradation Rate of NBDE Stabilized with 200ppm of BHT Using Accelerated Aging Conditions

Commercial samples of NBDE are typically stabilized with BHT. In thisexample, comparable experiments were carried out to evaluate thedegradation rate of NBDE when using BHT as the stabilizer.

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of BHT stabilizer. This is a common level of BHT present in NBDEas provided by chemical suppliers. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 80° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 2.64 wt. %, corresponding toa degradation rate of 179 ppm per hour at 80° C. This represents a 31%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIG. 3.

Example 5 Evaluation of the Degradation Rate of NBDE Stabilized with 200ppm of TBC Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of TBC (p-tert-butylcatechol) stabilizer. The stabilized NBDE wassubjected to accelerated aging test conditions by heating to 80° C. for7 days, followed by He purge to determine the amount of non-volatileresidue as described in Example 3. This test was run in duplicate. Theaverage non-volatile residue for these two runs was 2.64 wt. %,corresponding to a degradation rate of 157 ppm per hour at 80° C. Thisrepresents a 39.1% decrease in the degradation rate relative tounstabilized NBDE. The experimental results are summarized in Table 1and FIG. 3.

Example 6 Evaluation of the Degradation Rate of NBDE Stabilized with 200ppm of TBC Containing 8 Volume % Oxygen in the Headspace

The utilization of oxygen in combination with the stabilizer istypically done to enhance stability during chemical transport andstorage. This is accomplished by storing the polymerizable chemical in acontainer in which oxygen comprises 5-20% of the gas in the headspaceabove the stored liquid. In this manner, the oxygen dissolves in thehydrocarbon liquid and thus is available to facilitate the inhibition ofthe polymerization reaction. The oxygen can be diluted with an inert gassuch as nitrogen or helium to create the desired oxygen content in theheadspace gas. This is commonly done to ensure a non-flammableenvironment for the material being stabilized. Alternatively, anappropriate amount of ambient air can be introduced into the containerin order to establish the desired gaseous oxygen content.

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of TBC stabilizer. Approximately 170 g (˜200 ml) ofTBC-stabilized NBDE was added to a 500 ml quartz bubbler within anitrogen dry box as described in Example 1. The bubbler was removed fromthe dry box. Twenty five sccm (standard cubic centimeters) of nitrogenwas removed from the bubbler headspace using a syringe. Twenty five sccmof research grade oxygen was subsequently added to the headspace byreinjecting the gas into the bubbler. The NBDE bubbler thus prepared hadnominally 8 volume percent oxygen in the headspace. The sample wassubjected to accelerated aging test conditions by heating to 80° C. for7 days, followed by He purge to determine the amount of non-volatileresidue as described in Example 3. This test was run in duplicate. Theaverage non-volatile residue for these two runs was 0.97 wt. %,corresponding to a degradation rate of 57 ppm per hour at 80° C. Thisrepresents a 77.7% decrease in the degradation rate relative tounstabilized NBDE. The experimental results are summarized in Table 1and FIG. 3.

Example 7 Evaluation of the Degradation Rate of NBDE Stabilized with 200ppm of MHQ Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of MHQ (methyl hydroquinone) stabilizer. The stabilized NBDE wassubjected to accelerated aging test conditions by heating to 80° C. for7 days, followed by He purge to determine the amount of non-volatileresidue as described in Example 3. This test was run in duplicate. Theaverage non-volatile residue for these two runs was 0.79 wt. %,corresponding to a degradation rate of 47 ppm per hour at 80° C. Thisrepresents an 81.7% decrease in the degradation rate relative tounstabilized NBDE. The experimental results are summarized in Table 1and FIG. 3

Example 8 Evaluation of the Degradation Rate of NBDE Stabilized with 200ppm of MHQ Containing 5 Volume % Oxygen in the Headspace

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of MHQ stabilizer. Approximately 150 g (˜180 ml) ofMHQ-stabilized NBDE was added to a 500 ml quartz bubbler within anitrogen dry box as described in Example 1. The bubbler was removed fromthe dry box. Sixteen sccm (standard cubic centimeters) of nitrogen wasremoved from the bubbler headspace using a syringe. Sixteen sccm ofresearch grade oxygen was subsequently added to the headspace byreinjecting the gas into the bubbler. The NBDE bubbler thus prepared hadnominally 5 volume percent oxygen in the headspace. The stabilized NBDEwas subjected to accelerated aging test conditions by heating to 80° C.for 7 days, followed by He purge to determine the amount of non-volatileresidue as described in Example 3. This test was run in duplicate. Theaverage non-volatile residue for these two runs was 0.39 wt. %,corresponding to a degradation rate of 23 ppm per hour at 80° C. Thisrepresents a 91.1% decrease in the degradation rate relative tounstabilized NBDE. The experimental results are summarized in Table 1and FIG. 3.

Example 9 Evaluation of the Degradation Rate of NBDE Stabilized with 200ppm of HQMME Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of HQMME (hydroquinone monomethyl ether) stabilizer. Thestabilized NBDE was subjected to accelerated aging test conditions byheating to 80° C. for 7 days, followed by He purge to determine theamount of non-volatile residue as described in Example 3. This test wasrun in duplicate. The average non-volatile residue for these two runswas 0.90 wt. %, corresponding to a degradation rate of 53 ppm per hourat 80° C. This represents a 79.3% decrease in the degradation raterelative to unstabilized NBDE. The experimental results are summarizedin Table 1 and FIG. 3.

Example 10 Evaluation of the Degradation Rate of NBDE Stabilized with 50ppm of HQMME Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 50 ppm byweight of HQMME stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating it to 80° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate, using 111 g and130 g of NBDE for the two runs. The average non-volatile residue forthese two runs was 1.42 wt. %, corresponding to a degradation rate of 84ppm per hour at 80° C. This represents a 67.3% decrease in thedegradation rate relative to unstabilized NBDE. The experimental resultsare summarized in Table 1 and FIG. 3.

Example 11 Evaluation of the Degradation Rate of NBDE Stabilized with500 ppm of HQMME Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 500 ppm byweight of HQMME stabilizer. The stabilized NBDE (209 g) was subjected toaccelerated aging test conditions by heating to 80° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. The non-volatile residue for this run wasmeasured to be 1.73 wt. %, corresponding to a degradation rate of 103ppm per hour at 80° C. This represents a 60.1% decrease in thedegradation rate relative to unstabilized NBDE. The experimental resultsare summarized in Table 1 and FIG. 3.

Example 12 Evaluation of the Degradation Rate of NBDE Stabilized With200 ppm of 2-Hydroxy-4-Methoxybenzophenone (2H4MB) Using AcceleratedAging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of 2H4MB stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 80° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.33 wt. %, corresponding toa degradation rate of 20 ppm per hour at 80° C. This represents a 92.3%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 13 Evaluation of the Degradation Rate of NBDE Stabilized with200 ppm of 2,4-Dihydroxybenzophenone (24DHB) Using Accelerated AgingConditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of 24DHB stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 80° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.21 wt. %, corresponding toa degradation rate of 12 ppm per hour at 80° C. This represents a 95.2%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 14 Evaluation of the Degradation Rate of NBDE Stabilized with200 ppm of 2,2′-Dihyroxy-4-Methoxybenzophenone (22DH4MB) UsingAccelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of 22DH4MB stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 80° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.21 wt. %, corresponding toa degradation rate of 13 ppm per hour at 80° C. This represents a 95.1%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 15 Evaluation of the Degradation Rate of NBDE at 80° C.Stabilized with 200 ppm of TEMPO Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of TEMPO stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 80° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.02 wt. %, corresponding toa degradation rate of 1 ppm per hour at 80° C. This represents a 99.4%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 16 Evaluation of the Degradation Rate of NBDE at 80° C.Stabilized with 50 ppm of TEMPO Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 50 ppm byweight of TEMPO stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 80° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.04 wt. %, corresponding toa degradation rate of 3 ppm per hour at 80° C. This represents a 99.0%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 17 Evaluation of the Degradation Rate of NBDE at 80° C.Stabilized with 20 ppm of TEMPO Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 20 ppm byweight of TEMPO stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 80° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.10 wt. %, corresponding toa degradation rate of 6 ppm per hour at 80° C. This represents a 97.7%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 18 Evaluation of the Degradation Rate of NBDE at 80° C.Stabilized with 5 ppm of TEMPO Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 5 ppm byweight of TEMPO stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 80° C. for 6 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. The non-volatile residue for this run was 0.13wt. %, corresponding to a degradation rate of 9 ppm per hour at 80° C.This represents a 96.5% decrease in the degradation rate relative tounstabilized NBDE. The experimental results are summarized in Table 1and FIGS. 2 and 3.

Example 19 Evaluation of the Degradation Rate of NBDE at 80° C.Stabilized with 200 ppm of 4H-TEMPO Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of 4H-TEMPO stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 80° C. for 6 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.10 wt. %, corresponding toa degradation rate of 7 ppm per hour at 80° C. This represents a 97.2%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 20 Evaluation of the Degradation Rate of NBDE at 80° C.Stabilized with 20 ppm of 4H-TEMPO Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 20 ppm byweight of 4H-TEMPO stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 80° C. for 6 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.08 wt. %, corresponding toa degradation rate of 6 ppm per hour at 80° C. This represents a 97.8%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 21 Evaluation of the Degradation Rate of NBDE at 60° C.Stabilized with 200 ppm of TEMPO Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 200 ppm byweight of TEMPO stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 60° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.02 wt. %, corresponding toa degradation rate of 1 ppm per hour at 80° C. This represents a 99.5%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 22 Evaluation of the Degradation Rate of NBDE at 60° C.Stabilized with 50 ppm of TEMPO Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 50 ppm byweight of TEMPO stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 60° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.06 wt. %, corresponding toa degradation rate of 3 ppm per hour at 80° C. This represents a 98.7%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 23 Evaluation of the Degradation Rate of NBDE at 60° C.Stabilized with 20 ppm of TEMPO Using Accelerated Aging Conditions

A sample of NBDE was flash distilled to remove non-volatile impuritiesas described in Example 1. The distilled NBDE was spiked with 20 ppm byweight of TEMPO stabilizer. The stabilized NBDE was subjected toaccelerated aging test conditions by heating to 60° C. for 7 days,followed by He purge to determine the amount of non-volatile residue asdescribed in Example 3. This test was run in duplicate. The averagenon-volatile residue for these two runs was 0.03 wt. %, corresponding toa degradation rate of 2 ppm per hour at 80° C. This represents a 993%decrease in the degradation rate relative to unstabilized NBDE. Theexperimental results are summarized in Table 1 and FIGS. 2 and 3.

Example 24 Mixing of Aged Unstabilized NBDE with DEMS as a Polar Liquid

This example illustrates the forced precipitation of the non-polaroligomers by gradually increasing the net polarity of the liquid.Working in a nitrogen containing dry box, 102.0 g of unstabilized NBDEwhich had aged for 287 days at ambient temperature was placed into a 200ml Pyrex bottle. The same weight of DEMS was placed into a secondsimilar Pyrex bottle. Both the NBDE and DEMS were clear, colorlessliquids with no indication of precipitate or residue. The two liquidswere combined by slowly adding the DEMS to the NBDE. After the additionof about 20 g of DEMS a small amount of a white permanent precipitatewas evident in the DEMS-NBDE mixture. This precipitate grew moreprominent as the balance of the DEMS was added to the NBDE. The whiteprecipitate gradually settled to the bottom of the Pyrex container. Thecontents of the Pyrex container were transferred to a Schlenk flask. Theflask was subjected to dynamic vacuum for 4 hours at room temperature toremove the DEMS and NBDE liquids, leaving behind 1.20 g. of white solid.This weight of non-volatile solid residue corresponds to 1.18 wt. %based on the initial weight of the NBDE. This is equivalent to adegradation rate of 1.71 ppm per hour at ambient temperature. The weightpercent residue determined by this route is in excellent agreement withthe amount of residue measured by the He purge non-volatile residue testdescribed in FIGS. 2 and 3.

Example 25 Evaluation of Precipitation in the Mixing of AgedUnstabilized NBDE with DEMS

NBDE was flash distilled to remove non-volatile impurities using arotary-evaporator as described in Example 1. The distilled material wasanalyzed by GC to have a nominal purity of 99.4%. No stabilizer wasadded to the NBDE. The unstabilized NBDE was subjected to acceleratedaging test conditions by heating to 80° C. for 7 days in quartz bubblersas described in Example 3. This test was done in duplicate using 87.64 gand 90.23 g of NBDE for the two runs. Upon removal of the two bubblersfrom the oven at 80° C. there was no visible sign of precipitation ordiscoloration of the NBDE liquid. After allowing the NBDE to cool toroom temperature, DEMS was slowly added to each bubbler through theinlet line in an attempt to force the precipitation of dissolvedoligomeric degradation products. The first permanent precipitate wasvisible after the addition of 35-40 g of DEMS to the unstabilized NBDE.Additional DEMS was added until each bubbler contained a 1:1 weightratio of NBDE to DEMS. At this point a large amount of white precipitatewas evident, indicating that a substantial amount of oligomericdegradation products were present. The bubblers were subjected todynamic vacuum for 4 hours at 30° C., followed by a final evacuation for1 hour at 80° C., leaving behind 0.73 g and 1.04 g of white solidresidue. This amounts to an average non-volatile residue of 1.00% basedon the initial weight of the NBDE, corresponding to a degradation rateof 59 ppm per hour at 80° C.

Example 26 Evaluation of Reduction of Precipitation in the Mixing ofAged NBDE with DEMS Stabilized with 200 ppm of HQMME

NBDE was flash distilled to remove non-volatile impurities using arotary-evaporator as described in Example 1. The distilled material wasanalyzed by GC to have a nominal purity of 99.4%. The NBDE was spikedwith 200 ppm by weight of HQMME stabilizer. The stabilized NBDE wassubjected to accelerated aging test conditions by heating to 80° C. for7 days in quartz bubblers as described in Example 3. This test was donein duplicate using 98.77 g and 71.93 g of NBDE for the two runs. Uponremoval of the two bubblers from the oven at 80° C. there was no visiblesign of precipitation or discoloration of the NBDE liquid. Afterallowing the NBDE to cool to room temperature, DEMS was slowly added toeach bubbler through the inlet line in an attempt to force theprecipitation of dissolved oligomeric degradation products. The additionof DEMS continued until each bubbler contained a 1:1 weight ratio ofNBDE to DEMS. This resulted in a faint, cloudy solution in each of thetwo bubblers, indicating precipitation of a small amount of oligomersfrom solution. The bubblers were subjected to dynamic vacuum for 4 hoursat 30° C., followed by a final evacuation for 1 hour at 80° C., leavingbehind 0.17 g and 0.14 g of white solid residue. This amounts to anaverage non-volatile residue of 0.18 wt. % based on the initial weightof the NBDE, corresponding to a degradation rate of 11 ppm per hour at80° C. This represents an 82% decrease in the degradation rate relativeto forced precipitation of the unstabilized NBDE subjected to identicalageing conditions as described in Example 13. The experimental resultsare summarized in Table 2.

Example 27 Evaluation of Reduction of Precipitation in the Mixing ofAged NBDE with DEMS Stabilized with 200 ppm of MHQ

NBDE was flash distilled to remove non-volatile impurities using arotary-evaporator as described in Example 1. The distilled material wasanalyzed by GC to have a nominal purity of 99.4%. The NBDE was spikedwith 200 ppm by weight of MHQ stabilizer. The stabilized NBDE wassubjected to accelerated aging test conditions by heating to 80° C. for7 days in quartz bubblers as described in Example 3. This test was donein duplicate using 105.17 g and 98.53 g of NBDE for the two runs. Uponremoval of the two bubblers from the oven at 80° C. there was no visiblesign of precipitation or discoloration of the NBDE liquid. Afterallowing the NBDE to cool to room temperature, DEMS was slowly added toeach bubbler through the inlet line in an attempt to force theprecipitation of dissolved oligomeric degradation products. The additionof DEMS continued until each bubbler contained a 1:1 weight ratio ofNBDE to DEMS. The resulting NBDE-DEMS blend remained clear and colorlesswith no visible indication of precipitation. The bubblers were subjectedto dynamic vacuum for 4 hours at 30° C., followed by a final evacuationfor 1 hour at 80° C., leaving behind 0.10 g and 0.03 g of white solidresidue. This amounts to an average non-volatile residue of 0.06 wt.based on the initial weight of the NBDE, corresponding to a degradationrate of 4 ppm per hour. This represents a 94% decrease in thedegradation rate relative to forced precipitation of the unstabilizedNBDE subjected to identical ageing conditions as described in Example13. The experimental results are summarized in Table 2.

Example 28 Evaluation of Reduction of Precipitation in the Mixing ofAged NBDE with DEMS Stabilized with 200 ppm 22DH4MB

NBDE was flash distilled to remove non-volatile impurities using arotary-evaporator as described in Example 1. The distilled material wasanalyzed by GC to have a nominal purity of 99.4%. The NBDE was spikedwith 200 ppm by weight of 22DH4MB stabilizer. The stabilized NBDE wassubjected to accelerated aging test conditions by heating to 80° C. for7 days in quartz bubblers as described in Example 3. This test was donein duplicate using 111.53 g and 106.22 g of NBDE for the two runs. Uponremoval of the two bubblers from the oven at 80° C. there was no visiblesign of precipitation or discoloration of the NBDE liquid. Afterallowing the NBDE to cool to room temperature, DEMS was slowly added toeach bubbler through the inlet port in an attempt to force theprecipitation of dissolved oligomeric degradation products. The additionof DEMS continued until each bubbler contained a 1:1 weight ratio ofNBDE to DEMS. This resulted in a cloudy solution in each of the twobubblers, indicating some amount of precipitation of oligomers fromsolution. The bubblers were subjected to dynamic vacuum for 4 hours at30° C., followed by a final evacuation for 1 hour at 80° C., leavingbehind 0.51 g and 0.65 g of white solid residue. This equates to anaverage non-volatile residue of 0.53 wt. % based on the initial weightof the NBDE, corresponding to a degradation rate of 32 ppm per hour at80° C. This represents a 46% decrease in the degradation rate relativeto forced precipitation of the unstabilized NBDE subjected to identicalageing conditions as described in Example 25. The experimental resultsare summarized in Table 2.

Example 29 Evaluation of Reduction of Precipitation in the Mixing ofAged NBDE with DEMS Stabilized with 200 ppm of TEMPO

NBDE was flash distilled to remove non-volatile impurities using arotary-evaporator as described in Example 1. The distilled material wasanalyzed by GC to have a nominal purity of 99.4%. The NBDE was spikedwith 200 ppm by weight of TEMPO stabilizer. The stabilized NBDE wassubjected to accelerated aging test conditions by heating to 80° C. for7 days in quartz bubblers as described in Example 3. This test was donein duplicate using 94.77 g and 110.56 g of NBDE for the two runs. Uponremoval of the two bubblers from the oven at 80° C. there was no visiblesign of precipitation. After allowing the NBDE to cool to roomtemperature, DEMS was slowly added to each bubbler through the inletport in an attempt to force the precipitation of dissolved oligomericdegradation products. The addition of DEMS continued until each bubblercontained a 1:1 weight ratio of NBDE to DEMS. The resulting NBDE-DEMSblend remained clear with no visible indication of cloudiness orprecipitation. The bubblers were subjected to dynamic vacuum for 4 hoursat 30° C., followed by a final evacuation for 1 hour at 80° C., leavingbehind 0.11 g and 0.10 g of yellowish residue. This equates to anaverage non-volatile residue of 0.10 wt. % based on the initial weightof the NBDE, corresponding to a degradation rate of 6 ppm per hour. Thisrepresents a 90% decrease in the degradation rate relative to forcedprecipitation of the unstabilized NBDE subjected to identical ageingconditions as described in Example 25. The experimental results aresummarized in Table 2.

Example 30 Mixing of Aged Unstabilized NBDE with a Polar Solvent

Similar to Example 24, working in a nitrogen containing dry box, 2.0 ml(1.6 g) of isopropyl alcohol (IPA) was slowly added to 2.0 ml of theunstabilized NBDE (1.7 g). The NBDE used for this test was aged for 287days at ambient temperature. Both the NBDE and IPA used for thisexperiment were clear, colorless liquids with no indication ofprecipitate or residue. An immediate permanent precipitate was noticedafter the addition of the first few drops of isopropanol to the agedNBDE. The amount of precipitation became more pronounced as theremainder of the 2.0 ml of IPA was added. This example againdemonstrates the precipitation of the largely non-polar oligomers causedby increasing the net polarity of the solvent.

Example 31 Characterization of NBDE Degradation Products

A 50 g sample of unstabilized NBDE which had been stored at roomtemperature for several months was placed into a 100 ml quartz ampouleequipped with a Teflon valve. The ampoule was evacuated at roomtemperature for 2 hours to generate an off-white non-volatile residue.The resulting solid was collected and analyzed by solids-probe massspectrometry. The analysis confirmed the presence of various oligomersof NBDE, including the dimer, trimer, tetramer, pentamer, hexamer, etc.The solids-probe mass spectrum from this analysis is shown in FIG. 1.

TABLE 1 Summary of the non-volatile residue test results described inExamples 1-23. Degradation Normalized Reduction of Example Wt. of NBDENVR (non-volatile residue) rate degradation degradation No. StabilizerAging Conditions (g) (g) (wt. %) avg (wt. %) (ppm/hr) rate rate (%) 1 nostabilizer none 619.32 0.59 0.10 0.05 NA NA NA 582.70 0.00 0.00 2 nostabilizer 287 days at RT 202.46 2.29 1.13 1.12 1.63 NA NA 202.15 2.241.11 3 no stabilizer 7 days at 80° C. 148.35 6.25 4.21 4.33 258 1.0000.0 149.79 6.06 4.05 103.87 5.59 5.38 118.95 5.94 4.99 148.30 5.31 3.58149.15 5.65 3.79 4 200 ppm 7 days at 80° C. 149.44 4.6 3.08 3.01 1790.690 31.0 BHT 163.89 4.83 2.95 5 200 ppm 7 days at 80° C. 155.43 3.432.21 2.64 157 0.609 39.1 TBC 154.63 4.75 3.07 6 200 ppm 7 days at 80° C.174.10 1.51 0.87 0.97 57 0.223 77.7 TBC with O₂ 164.59 1.75 1.06 7 200ppm 7 days at 80° C. 154.95 1.14 0.74 0.79 47 0.183 81.7 MHQ 146.14 1.240.85 8 200 ppm 7 days at 80° C. 152.93 0.52 0.34 0.39 23 0.089 91.1 MHQwith O₂ 145.57 0.63 0.43 9 200 ppm 7 days at 80° C. 106.26 1.00 0.940.90 53 0.207 79.3 HQMME 114.82 0.98 0.85 10 50 ppm 7 days at 80° C.110.75 1.20 1.08 1.42 84 0.327 67.3 HQMME 130.23 2.28 1.75 11 500 ppm 7days at 80° C. 209.14 3.62 1.73 1.73 103 0.399 60.1 HQMME 12 200 ppm 7days at 80° C. 147.78 0.59 0.40 0.33 20 0.077 92.3 2H4MB 154.91 0.410.26 13 200 ppm 7 days at 80° C. 149.14 0.32 0.21 0.21 12 0.048 95.224DHB 145.25 0.29 0.20 14 200 ppm 7 days at 80° C. 152.00 0.31 0.20 0.2113 0.049 95.1 22DH4MB 165.88 0.37 0.22 15 200 ppm 7 days at 80° C.140.51 0.04 0.03 0.02 1 0.006 99.4 TEMPO 148.59 0.03 0.02 16 50 ppm 7days at 80° C. 143.38 0.08 0.06 0.04 3 0.010 99.0 TEMPO 139.63 0.04 0.0317 20 ppm 7 days at 80° C. 130.45 0.17 0.13 0.10 6 0.023 97.7 TEMPO144.58 0.10 0.07 18 5 ppm 6 days at 80° C. 68.82 0.09 0.13 0.13 9 0.03596.5 TEMPO 19 200 ppm 6 days at 80° C. 137.56 0.12 0.09 0.10 7 0.02897.2 4H-TEMPO 116.36 0.14 0.12 20 20 ppm 6 days at 80° C. 130.98 0.150.11 0.08 6 0.022 97.8 4H-TEMPO 102.25 0.05 0.05 21 200 ppm 7 days at60° C. 130.38 0.03 0.02 0.02 1 0.005 99.5 TEMPO 172.71 0.03 0.02 22 50ppm 7 days at 60° C. 147.10 0.12 0.08 0.06 3 0.013 98.7 TEMPO 155.900.05 0.03 23 20 ppm 7 days at 60° C. 154.92 0.03 0.02 0.03 2 0.007 99.3TEMPO 167.67 0.07 0.04

TABLE 2 Summary of the non-volatile residue test results from the forcedprecipitation experiments described in Examples 25-29. Wt. of Wt. ofDegradation Normalized Reduction of Example Ageing NBDE DEMS NVR(non-volatile residue) rate degradation degradation No. StabilizerConditions (g) added (g) (g) (wt. %) avg (wt. %) (ppm/hr) rate rate (%)25 none 7 days at 87.64 87.64 1.04 1.19 1.00 59 1.00 0.00 80° C. 90.2390.23 0.73 0.81 26 200 ppm 7 days at 98.77 98.77 0.17 0.17 0.18 11 0.180.82 HQMME 80° C. 71.93 71.93 0.14 0.19 27 200 ppm 7 days at 94.77 94.770.10 0.10 0.06 4 0.06 0.94 MHQ 80° C. 110.56 110.56 0.03 0.03 28 200 ppm7 days at 111.53 111.53 0.51 0.46 0.53 32 0.54 0.46 22DH4MB 80° C.106.22 106.22 0.65 0.61 29 200 ppm 7 days at 94.77 94.77 0.11 0.12 0.106 0.10 0.90 TEMPO 80° C. 110.56 110.56 0.10 0.09

The embodiments of the present invention listed above, including theworking examples, are exemplary of numerous embodiments that may be madeof the present invention. It is contemplated that numerous otherconfigurations of the process may be used, and the materials used in theprocess may be selected from numerous materials other than thosespecifically disclosed. In short, the present invention has been setforth with regard to particular embodiments, but the full scope of thepresent invention should be ascertained from the claims as follow.

1. A method for stabilizing an unsaturated hydrocarbon-based precursor material against its polymerization comprising steps of: providing the unsaturated hydrocarbon-based precursor material; and adding to the unsaturated hydrocarbon-based precursor material at least one nitroxyl radical based stabilizer; wherein the unsaturated hydrocarbon-based precursor material is selected from the group consisting of 2,5-Norbornadiene (NBDE), Norbornene, and mixtures thereof; and the at least one nitroxyl radical based stabilizer has a structure of:

wherein: raised period “•” denotes one unpaired electron; R¹ through R⁴ are independently selected from a straight chained or branched, substituted or unsubstituted, alkyl or alkenyl group; wherein the substituted group comprises oxygen-containing groups selected from the group consisting of hydroxyl, carbonyl, alkoxide, and carboxylic group; and R⁵ and R⁶ are independently selected from a straight chained or branched, a substituted or unsubstituted, alkyl group or alkenyl group.
 2. The method of claim 1, wherein the unsaturated hydrocarbon-based precursor material is 2,5-Norbornadiene (NBDE).
 3. The method of claim 1, wherein the alkyl group or the alkenyl group in R⁵ and R⁶ is connected by a bridging group to form a cyclical structure of saturated, partially unsaturated or aromatic ring.
 4. The method of claim 1, wherein R¹ through R⁴ each is selected from the group consisting of methyl, ethyl, n-propyl, n-butyl, n-pentyl, iso-propyl, iso-butyl, iso-pentyl, tert-butyl, neo-pentyl, octadecyl, propenyl, butenyl, pentenyl and combinations thereof.
 5. The method of claim 1, wherein R⁵ and R⁶ each is selected from the group consisting of methyl, ethyl, n-propyl, n-butyl, n-pentyl, iso-propyl, iso-butyl, iso-pentyl, tert-butyl, neo-pentyl, octadecyl, propenyl, butenyl, pentenyl, and part of a cyclic structure and its substituted cyclic structure of 6-membered piperidine or 5-membered pyrrolidones.
 6. The method of claim 1, wherein the nitroxyl radical based stabilizer selected from the group consisting of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (4H-TEMPO), di-tert-butyl nitroxyl, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-one, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl acetate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 2-ethylhexanoate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl stearate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl benzoate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 4-tert-butylbenzoate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)succinate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)sebacate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)n-butylmalonate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)phthalate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)isophthalate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)terephthalate, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)hexahydroterephthalate, N,N′-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipamide, N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-caprolactam, N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-dodecylsuccinimide, 2,4,6-tris(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl isocyanurate, 2,4,6-tris-[N-butyl-N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl]-s-triazine, 4,4′-ethylenebis(1-oxyl-2,2,6,6-tetramethylpiperazin-3-one) and combinations thereof.
 7. The method of claim 1, wherein the nitroxyl radical based stabilizer selected from the group consisting of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (4H-TEMPO).
 8. The method of claim 1, further comprising a step of adding to the unsaturated hydrocarbon-based precursor material at least one polar liquid.
 9. The method of claim 8, wherein the at least one polar liquid is selected from the group consisting of diethoxymethylsilane (DEMS), isopropanol (IPA) and mixtures thereof. 